Refresher Programme for Geography Teachers Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions Chan Lung Sang Department of Earth Sciences Faculty of Science, HKU 地地 ( 地地地地地地地地地地地地地地地地地地地地 ) 地地 ( 地地地地地地 ) 地地 ( 地地地地地地地地地地地地地地地地地地地 ) Landform and Endogenetic Processes Part 1: Plate Tectonics • History of Development • Basic Concepts – – – – – Earth’s interior model Crustal provinces & structures Rock formation Energy sources Mineral and oil formation • Tectonics and Geology of Hong Kong Region [MANY OF THE FIGURES USED IN THIS PRESENTATION WERE DOWNLOADED FROM THE INTERNET THEIR CREATORS , OFTEN ANONYMOUS, ARE GRATEFULLY ACKNOWLEDGED] From Continental Drift to Plate Tectonics Alfred Wegener • • • • Paleoclimate Fossil evidence Geological evidence Coastline geometry Birth of the Plate Tectonics Theory Plate tectonics theory was founded upon the following new findings in the late 1960s: • Ocean floor topography • Marine magnetic anomalies • Paleomagnetism & geomagnetic field reversals • Sea floor spreading Plate Boundaries, Earthquakes and Major Volcanoes of the World * Note new designation of plate boundary at Japan Plate Boundaries * Note associated landforms: axial rift at mid-ocean ridge, sea trench at subduction zone, sea mounts and island arc A paradigm shift - A unifying theory accounting for •Earth’s interior structure •Origin of atmosphere & hydosphere •Crustal structures and provinces •Volcanism & earthquakes •Rock record •Fossil record •Sedimentary basins •Petroleum and mineral formation •Geophysical fields Rock Formations Rock Cycle in Plate Tectonics Context Igneous & Metamorphic Rocks * Most magmas form from melting of mantle and crustal material in the overriding plate and not the descending plate Ophiolite: suite of oceanic crust and mantle rocks Pillow basalt intruded by mafic dikes, Cyprus *What formerly called geosynclines are now known to be mountains that formed in active continental margins *The term should not be used anymore The Obsolete Concept of Geosyncline The Energy Source Earth’s Source of Energy • • • • Primordial heat Radioactivity Gravitational heat Phase changes * Phase change, not radioactivity, is the primary energy source for plate motion Outer Core-Inner Core Relation Outer core condenses gradually to become part of inner core The process probably involves also a compositional change Mantle Convection heat energy from core 地地地地 地地地地地地 * Not all spreading ridges are located above mantle divergence Mineral and oil Formations ACTIVE VS PASSIVE MARGIN ACTIVE MARGIN PASSIVE MARGIN • • Stable • Wide continental shelf • Continental crust thins out gradually • Oil and gas resources • magmatic activity mountain belt with thick continental crust • narrow continental shelf • active seismicity • mineral deposit Tectonic Evolution of Hong Kong Region Geological Map of Hong Kong (Geological Survey, GEO) Department of Earth Sciences, HKU http://www.hku.hk/earthsci End of Part chanls@hku.hk Department of Earth Sciences, University of Hong Kong Useful Web Links pubs.usgs.gov/publications/text/dynamic.html geology.er.usgs.gov/eastern/tectonic.html www.school.discovery.com www.geolsoc.com.hk [...]... 2890-4600 F OC-IC Transition 4600-5160 G Inner Core 5160-6370 solid Mg-rich silicate (olivine) near melting solid soild (softer) FeS+Fe Fe+FeO liquid liquid+solid solid Earlier idea on crustal structure * The concepts of sial and sima are old and imprecisely describe current understanding of crustal structure *Lithosphere includes the crust and part of the upper mantle Asthenosphere is not a molten layer *Note